Babies head measuring 2weeks ahead

I'm 33weeks and my babies head is measuring approx 2 weeks ahead on sonogram. There is not fluid or blood in his skull and accorindg to the doctor everything is normal except for his head measuring larger.  I just hope my son is healthy and that he will fit vaginally. Has anyone else had this happen before? Did everything turn out fine? Could the sonogram be inaccurate?